We propose to investigate molecular mechanisms that underlie individual differences in psychological well-being (PWB). PWB is a multidimensional construct that encompasses positive emotion, life satisfaction, and sense of purpose and meaning in life, and is more than the absence of negative emotional states. Many prospective longitudinal studies have shown that PWB is associated with better mental and physical health after adjusting for negative emotion and other relevant confounding factors. Indeed, PWB mitigates risks of having suicide ideation, depression, substance abuse, post-traumatic stress disorder, Alzheimer's dementia, heart disease, diabetes, and reduces all-cause mortality. Notably, PWB has a substantial genetic contribution with a heritability of approximately 64%. However, the genetic mechanisms of PWB are largely unknown despite its many important benefits. To address this, we recently performed a genome-wide association study (GWAS) of positive emotion, a major facet of PWB. We found a single nucleotide polymorphism (SNP), rs322931, significantly associated with positive emotion at genome-wide level. This association has since been replicated in two independent datasets. We subsequently found that rs322931 is a cis-expression quantitative trait locus (eQTL) for microRNAs 181a and 181b (miR-181a/b) expressed in human blood and brain. Intriguingly, miR-181a/b are enriched in the reward-motivation neural circuit and regulate synaptic plasticity and immune functioning in animal studies. Taken together, we hypothesize that miR-181a/b play a role in PWB. Given these exciting data, we propose to validate and extend our findings, leveraging already collected human post-mortem brain transcriptomic, epigenomic, proteomic, and genomic data to elucidate molecular mechanisms of PWB. This unique human brain dataset of 675 individuals, gathered by the NIH-funded Rush Memory and Aging Project (MAP) over 20 years, provides a rare opportunity to investigate mechanisms of PWB in the relevant organ, i.e. human brain, with 90% power for our proposed analyses. To that end, we propose the following aims. Aim 1 will validate the genetic findings from our GWAS of positive emotion in 2040 Veterans and MAP participants. Aim 2 will extend our findings by investigating the contribution of brain microRNAs in PWB using both a hypothesis-driven and hypothesis-neutral approach. Notably, microRNAs are important post-transcriptional regulators of gene expression and collectively regulate more than half of the protein-coding genes. Aim 3 will employ innovative systems biology approaches to identify gene networks and key expression regulatory drivers of PWB, as well as determine whether their protein levels are correspondingly altered in PWB. In sum, this novel and innovative proposal capitalizes on previously collected Veteran genetic samples and human post-mortem brain ?omic? data from the unique NIH-funded MAP cohort recruited over the last 20 years. We plan to combine these data with the ones we will generate and analyze them with innovative systems biology approaches to elucidate molecular mechanisms of PWB. We aspire to elucidate the genetic architecture of PWB to contribute to future efforts in developing biomarker based screening for risk stratification and intervention to enhance PWB and its beneficial effects.